To make your hypothesis an "If/Then" statement, you will need to add a small part at the beginning of your original hypothesis so that it sounds like "If I do this to my variables, then this will happen because ..." For yours, it could be "If I leave bread, cheese, and strawberries in the open air, then the strawberries will mold the fastest because..." The first part could be different depending on how you plan to let your foods mold. Hope this helps and if you have any more questions, feel free to ask.

Writing a hypothesis as an If/Then statement is used to formalize them. In your case, I believe that writing your hypothesis as an If/Then statement would look something like: If preservative level is related to molding, then strawberries will mold the fastest because they do not contain as many preservatives as bread or cheese.